Light source including means for translational movement of glow discharge along envelope axis



Oct. 15, 1968 J.J. MURAY 3,406,315

LIGHT SOURCE INCLUDING MEANS FOR TRANSLATIONAL MOVEMENT OP GLOW DISCHARGE ALONG ENVELOPE AXIS Filed Dec. 13, 1966 2 Sheets-Sheet 1 1.0-- g E E .a-- E 1-- I 5 R k, 5 .4 g .5 E .2--

soo 600 1000 I200 e00 600 moo 1200 ANODE POTENTIAL (VOLTS) ANODE POTENTIAL (VOLTS) figure 3 igure 4 INVENTOR JULIUS d. MURAY Q-C- sink ATTORNEY Oct. 15, 1968 LIGHT SOURCE INCLUDING MEANS FOR TRANSLATIONAL MOVEMENT OF GLOW DISCHARGE ALONG ENVELOPE AXIS Filed Dec. 13, 1966 2 Sheets-Sheet 2 42 42 36 c 3 Q l L 40 52 I 46 -o- -v Y- k 48 i a 48 i i 9 u re 5 INVENTOR JULIUS J. MURAY BY acswixk ATTORNEY J. J. MURAY 3,406,315

United States Patent C i 3,406,315 LIGHT SOURCE INCLUDING MEANS FOR TRANS- LATIONAL MOVEMENT OF GLOW DISCHARGE ALONG ENVELOPE AXIS Julius J. Muray, Los Altos, Calif., assignor to Hewlett- Packard Company, Palo Alto, Calif., a corporation of California Filed Dec. 13, 1965, Ser. No. 513,494 11 Claims. (Cl. 315334) ABSTRACT OF THE DISCLOSURE A wire anode and a multiple element cathode structure are coaxially supported within a gas-filled enclosure to provide a high stability light source.

This invention relates to high stability light sources and has as its main object the provision of an efficient low pressure light source which has a constant light output over a wide range of temperatures.

This object is accomplished according to the illustrated embodiment of the present invention by providing in an enclosure filled With a gas at low pressure a pair of generally cup-shaped electrodes which are spaced a finite distance apart and which are supported in face-to-face re lationship about a central wire electrode. The cup-shaped electrodes are each biased to a potential more negative than the potential of the central wire electrode so as to trap electrons and compel them to oscillate in the emitting region defined around the central wire electrode between the cup-shaped electrodes. These electron oscillations produce a discharge which is stabilized by the electrostatic field in the emitting region so as to emit a steady stream of light from between the cup-shaped electrodes.

Other and incidental objects of this invention will become apparent from a reading of this specification and an inspection of the accompanying drawing in which:

FIGURE 1 is a schematic diagram of a light source according to one embodiment of this invention;

FIGURE 2 is a perspective view of the electrode structure of the light source of FIGURE 1;

FIGURE 3 is a plot of the anode current-voltage characteristic of the light source of FIGURE 1;

FIGURE 4 is a plot of the light output versus the anode voltage for the light source of FIGURE 1;

FIGURE 5 is a schematic diagram of a light source according to another embodiment of this invention; and

FIGURE 6 is a perspective view of the electrode structure of the light source of FIGURE 5.

Referring to FIGURES l and 2, there is shown a transparent quartz enclosure 10 which is filled with a gas such as air or one of the noble gases at a low pressure in the range of Illto 10- torr (mm. Hg). A small-diameter wire anode 12 comprising, for example, a tungsten wire 1.3 x 10* millimeters in diameter is supported centrally within the enclosure 10 by standard means 14. Additionally, a pair of generally cup-shaped cathodes 16 is supported within the gas-filled enclosure 10 by standard means 18. These cup-shaped cathodes 16 are spaced a fixed distance apart and are supported in fact-to-tace relationship coaxially with the central wire anode 12. The cup-shaped cathodes 16 comprise, for example, identical stainless steel cylinders 1.2 centimeters in diameter. A bias terminal 20 positioned outside the gas-filled enclosure 10 is electrically connected to the wire anode 3,495,315 Patented Oct. 15, 1968 ice 12. Similarly, a pair of bias resistors 22 positioned outside the gas-filled enclosure 10 electrically connects each cup-shaped cathode 16 to a separate bias terminal 24. A source of potential indicated by the plus (-1-) and the minus polarity symbols in FIGURE 1 is connected to each of the bias terminals 20 and 24 to bias the cupshaped cathodes 16 to a potential more negative than the central wire anode 12. Thus, the cup-shaped cathodes 16 function as electron mirrors which trap electrons around the central wire anode 12 and compel the trapped elec trons to oscillate with minimal electron loss in the emitting region defined around the central wire anode 12 between the cup-shaped cathodes 16. These electron oscillations effectively cause ionization and excitation of gas molecules in the emitting region and thereby produce a discharge 26. The electrostatic field produced between the cup-shaped cathodes 16, which are negatively biased with respect to the wire anode 12, stabilizes the position of this discharge 26 in the emitting region at the place of weakest electrostatic field strength. Thus, by biasing the cup-shaped cathodes 16 to the same negative potential with respect to the Wire anode potential the discharge 26 is stably centered in the open space between the opposite faces of the identical cup-shaped cathodes 16 so as to emit a steady stream of light through the transparent enclosure 10.

The configuration of the central wire anode 12 and the cup-shaped cathodes 16 makes the probability of electron escape from the emitting region low and the probability of excitation of gas molecules in the emitting region high. 7

output is substantially independent of temperature. Thus,

a highly efiicient low-pressure light source is provided which in addition to being highly stable because of the stability of the discharge 26 provides a constant light output over a wide range of temperatures.

The wire anode voltage-current characteristic of a light source constructed as described above and filled with air at 10 torr pressure is shown in FIGURE 3. For the same light source the light output is shown plotted in arbitrary units versus the wire anode voltage in FIG- URE 4. The spectral response of the emitted light depends primarily on the gas used to fill the enclosure 10 and the pressure at which the gas is maintained. For example, the discharge 26 is a stabilized glow between the cup-shaped cathodes 16 when the light source is filled with air at 10- torr pressure, but is a luminous plasma sheet around the central wire anode 12 when the light source is filled with air at lower pressures.

The light source of this invention may also be operated in a pulsed mode in which the duration of the output light pulse can be controlled by a pulsing voltage 28 applied to one of the cup-shaped cathodes 16, as indicated at 30 in FIGURE 1. When operated in this pulsed mode the light source can be used as a voltage to light transducer in which the rise-time and duration of the output light pulse may be varied over a wide range by varying the pulsing voltage 28 applied to the selected cup-shaped cathode 16. The frequency response of the light source during operation in this pulsed mode is a function of the mobility of the gas used.

As already described above, when each of the cupshaped cathodes 16 is biased to the same negative potential with respect to the wire anode potential the discharge 26 is stably centered in the open space between the opposite faces of the cup-shaped cathodes 16. However, when the cup-shaped cathodes 16 are not biased to the same potential with respect to the wire anode 12 the discharge 26 moves in the direction of the lower electrostatic field and actually moves inside the corresponding cup-shaped cathode as, for example, is indicated by the dashed circle 32. The steering potential required to move the discharge 26 in this manner is only a few volts. This feature of the light source makes it useful as a voltage comparator. The position of the discharge in the emitting region serves to provide a visual indication of the voltage comparison much the same as conventional nulling devices.

Referring now to FIGURES and 6, there is shown another embodiment of the light source comprising a wire anode 34 centrally supported within a gas filled enclosure 36 by standard means 38. A pair of generally plate-shaped cathode elements 40 is supported within the gas-filled enclosure 36 by standard means 41. These plate-shaped cathode elements 40 are spaced a fixed distance apart and are supported in face-to-face relationship coaxially with the central wire anode 34. A plurality of n cylindrical cathode elements 42 is also supported within the gas-filled enclosure 36 by standard means 44. These cylindrical cathode elements 42 are spaced a fixed distance apart between the plate-shaped cathode elements 40 and are supported coaxially with the central wire anode 34. A bias terminal 46 positioned outside the gas-filled enclosure 36 is electrically connected to the wire anode 34. Similarly a plurality of n+2 resistors 48 positioned outside the gas-filled enclosure 36 electrically connect each of the cathode elements 40 and 42 to a separate bias terminal 50. A source of potential indicated by the and the minus polarity symbols in FIGURE 5 is connected to each of the bias terminals 46 and 50 to bias each of the cathode elements 40 and 42 to a potential more negative than the potential of the wire anode 34. The plate-shaped cathode elements 40 and the cylindrical cathode elements 42 function in the same manner as described above in connection with FIGURES 1 and 2, where a plate-shaped cathode element and a cylindrical cathode element were combined to form a single cup-shaped cathode 16. Thus, the cathode elements 40 and 42 provide a stabilized discharge 52 at the position of weakest electrostatic field strength in the emitting region define-d around the central wire anode 34 between the plate-shaped cathode elements 40. The cathode configuration of this light source makes it useful in applications where, for example, it is desired to accelerate the discharge 52 or perform a switching function. This may be done by appropriately adjusting the bias potential supplied to selected ones of the cylindrical cathode elements 42. A light source such as this may be used to provide a more sophisticated voltage comparator than the light source described above in connection with FIGURES 1 and 2.

I claim:

1. A low pressure light source for providing a substantially constant light output over a wide range of temperatures, said light source comprising:

a gas-filled enclosure;

21 wire electrode supported within said enclosure, said wire electrode being biased to a selected potential;

a first pair of adjacent electrode elements supported within said enclosure in face-to-face relationship about said wire electrode, the electrode elements of said first pair being spaced a fixed distance apart along said wire electrode and lying generally in a pair of planes intersecting said wire electrode;

a second pair of electrode elements supported Within said enclosure in face-to-face relationship about said end pair being spaced a fixed distance apart between wire electrode, the electrode elements of said secsaid first pair and encircling said wire electrode and an emitting region defined around said wire electrode between the adjacent electrode elements of said first pair; and

means for biasing each of said electrode elements of said first and second pairs to a negative potential with respect to the potential of said wire electrode for causing electron oscillations in the emitting region to produce a light emissive discharge in said region, whereby the position of the discharge along said wire electrode depends upon the potential difference between said electrode elements. 2. A low-pressure light source as in claim 1 wherein each of said electrode elements is biased to the same negative potential with respect to said wire electrode 'for centering said discharge in said emitting region.

3. A low-pressure light source as in claim 1, wherein selected ones of said electrode elements are biased at least momentarily to different potentials for positioning said discharge nearest the one of said electrode elements which is biased to the least negative potential with respect to the potential of said wire electrode.

4. A low-pressure light source as in claim 1, including means for altering the bias potential of at least one of said electrode elements.

5. A low-pressure light source as in claim 1 including at least one additional electrode element similar to those of said second pair, said additional electrode element being supported within said enclosure between an electrode element of said first pair and an electrode element of said second pair, said additional electrode element also being spaced a fixed distance from each of the electrode elements of said second pair and encircling said wire electrode and the emitting region. I

6. A low-pressure light source as in claim 1 wherein said electrode elements are coaxiall-y supported about said wire electrode.

7. A low-pressure light source for providing a substantially constant light output over a wide range of temperatures, said light source comprising:

a gas-filled enclosure;

a wire electrode supported within said enclosure, said wire electrode being biased to a selected potential;

a pair of generally cup-shaped electrodes supported within said enclosure in face-to-face relationship about said wire electrode and spaced a fixed distance apart along said wire electrode;

said pair of cup-shaped electrodes including a pair of adjacent end portions supported a fixed distance apart in face-to-face relationship, said pair of adiacent end portions lying generally in a pair of planes intersecting said wire electrode;

said pair of cup-shaped electrodes further including a pair of side portions supported a fixed distance apart in face-to-face relationship between said pair of end portions, said pair of side portions encircling said wire electrode and an emitting region defined around said wire electrode between said pair of end portions; and

means for biasing each of said cup-shaped electrodes to a negative potential with respect to the potential of said wire electrode for causing electron oscillations in the emitting region to produce a light emissive discharge in said region, whereby the position of the discharge along said wire electrode depends upon the potential difference between said electrode elements.

8. A low-pressure light source as in claim 7 wherein each of said cup-shaped electrodes is biased to the same negative potential with respect to said wire electrode for centering said discharge in said emitting region.

9. A low-pressure light source as in claim 7 wherein a selected one of said cup-shaped electrodes is biased at least momentarily to a different potential for positioning said discharge nearest the one of said cup-shaped elec- 5 trodes which is biased to the least negative potential with respect to the potential of said wire electrode.

10. A low-pressure light source as in claim 7 including means for altering the bias potential of at least one of said cup-shaped electrodes.

11. A low-pressure light source as in claim 7 wherein said cup-shaped electrodes are coaxially supported about said wire electrode.

References Cited UNITED STATES PATENTS 1,763,108 6/1930 Spencer 313-l88 JAMES w. LAWRENCE, Primary Examiner.

P. C. DEMEO, Assistant Examiner.

U.S. DEPARTMENT OF COMMERCE PATENT OFFICE Washington, D.C. 20231 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,406, 319 October 15 1961 Kenneth Milford Faulkes It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, line 10, 16,059/60 should read 16,059/53 Signed and sealed this 10th day of March 1970.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

